The present invention relates to the control of internal combustion engines. More specifically, the present invention relates to a method and apparatus to provide a variable indicative of torque in a variable displacement internal combustion engine for an automatic transmission control system.
Present regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in present vehicles. These regulatory conditions must be balanced with the demands of a consumer for high performance and quick response for a vehicle. Variable displacement internal combustion engines (ICEs) provide for improved fuel economy and torque on demand by operating on the principal of cylinder deactivation. During operating conditions that require high output torque, every cylinder of a variable displacement ICE is supplied with fuel and air (also spark, in the case of a gasoline ICE) to provide torque for the ICE. During operating conditions at low speed, low load and/or other inefficient conditions for a fully-displaced ICE, cylinders may be deactivated to improve fuel economy for the variable displacement ICE and vehicle. For example, in the operation of a vehicle equipped with an eight cylinder variable displacement ICE, fuel economy will be improved if the ICE is operated with only four cylinders during low torque operating conditions by reducing throttling losses. Throttling losses, also known as pumping losses, are the extra work that an ICE must perform to pump air around the restriction of the throttle and from the relatively low pressure of the intake manifold through the engine and out to the atmosphere.
The cylinders that are deactivated will not allow air flow through their intake and exhaust valves, reducing pumping losses by forcing the ICE to operate at a higher intake manifold pressure. Since the deactivated cylinders do not allow air to flow, additional losses are avoided by operating the cylinders as xe2x80x9cair springsxe2x80x9d due to the compression and decompression of the air in each deactivated cylinder.
For vehicles equipped with an automatic transmission, the deactivation of cylinders for a variable displacement ICE and the corresponding changes in air flow and torque must be coordinated with the operation of the automatic transmission. Traditionally, an automatic transmission control system will receive a throttle area or a throttle position variable that is indicative of the torque output of an ICE. The throttle position or area is used by a transmission control system as an indication of how much torque the ICE produces and is used in gear selection and stabilization of transmission shifts. In a variable displacement ICE, the throttle position will change when the variable displacement ICE is in partial and full displacement to produce the same torque. Thus, with variable displacement ICEs, throttle position/area no longer represents a unique engine torque value, making throttle position/area alone an insufficient load or torque variable.
The present invention is a method and apparatus that produces a throttle load variable for a variable displacement ICE that is independent of the displacement of the ICE. In the preferred embodiment of the present invention, an eight-cylinder internal combustion engine (ICE) may be operated as a four-cylinder engine by deactivating four cylinders. The cylinder deactivation occurs as a function of load or torque demand by the driver. An engine or powertrain controller will determine if the ICE should enter four-cylinder mode by monitoring the load and torque demands of the ICE. If the ICE is in a condition where it is inefficient to operate with the full complement of eight cylinders, the controller will deactivate the mechanisms operating the valves for the selected cylinders and also shut off fuel (and possibly spark in the case of a gasoline engine) to the cylinders. The deactivated cylinders will thus function as air springs to reduce throttling or pumping losses.
As previously described, the transition from eight cylinders to four cylinders or four cylinders to eight cylinders will create changes in the air flow through the throttle plate into the ICE that also affect the torque output of the ICE. The present invention generates a throttle plate position/area signal for an automatic transmission or powertrain controller that represents the torque output of the ICE independent of the displacement of the engine. The present invention includes software having a plurality of function blocks that calculate the desired throttle position/area for varying displacements of the ICE. These function blocks will simultaneously operate and generate the throttle area/position variable, and the engine or powertrain controller will determine the correct throttle area/position command to be used, depending on the displacement of the ICE. Accordingly, a throttle position/area command will always be calculated for a fully-displaced engine and may be used as a load variable for a transmission or powertrain controller.